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Depreciation and Amortization - Depreciation and Amortization Expense Excluded from Operating Expenses (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Component of Operating Other Cost and Expense [Line Items]      
Depreciation and amortization $ 296,083 $ 299,639 $ 312,703
Direct expenses [Member]
      
Component of Operating Other Cost and Expense [Line Items]      
Depreciation and amortization 277,662 283,720 297,517
General and administrative expenses [Member]
      
Component of Operating Other Cost and Expense [Line Items]      
Depreciation and amortization 4,137 4,224 5,033
Corporate expenses [Member]
      
Component of Operating Other Cost and Expense [Line Items]      
Depreciation and amortization $ 14,284 $ 11,695 $ 10,153